1. Field of the Invention
This invention relates generally to a device for use in demolishing, by using the reciprocal movement of an edge, a consolidated and hardened slurry body remaining in the form of a wall along the sidewalls of the hold of an iron-ore carrier, and more particularly to a device used in a wet-loading and dry-unloading method for iron-ore loaded in a slurry state in the carrier hold.
2. Description of the Prior Art
Before proceeding with the description of the present invention, it may be of assistance for a better understanding of the features of the invention to give a detailed description of the background of the so-called "wet-loading and dry-unloading system" used in transporting iron-ore in a slurry state from a mine via ocean to a refinery, including the use of an iron-ore transport ship or carrier.
Heretofore, two types of iron-ore transportation systems have been proposed, one being called the "dry-loading and dry-unloading system", and the other being referred to as a "wet-loading and wet-unloading system".
The iron-ore as used herein refers to a magnetite of a lower iron content, which is supplied in a fine powder after being crushed and dressed by a known method.
The size of this fine powder is that of about 44 .mu. particles, which usually amounts to about 80% of the total amount of the iron-ore. Because of its very fine size and poor water permeability, this kind of iron-ore causes a number of troublesome and hence uneconomical problems in providing for surface transportation, that is, in the land and sea transportation thereof.
For simplifying the description, the disadvantages or problems associated with the above two transportation systems will be enumerated below according to the type of system.
A. Dry-loading and dry-unloading system
In this system which has long been practiced, iron-ore is transported by land carrier, such as trucks or railroad, from a mine to a shipping harbor, where a huge ore transport ship or carrier, such as one having a load displacement of about 160,000 tons is loaded with the dry ore by belt conveyors or the like. Then, when the ore carrier arrives at an unloading harbor, the dry ore is unloaded by a crane or the like after the carrier has approached the quay. The disadvantages of this system are as follows:
1. The transportation expense is extremely high because of the use of such land transportation as trucks or railroads;
2. Large scale harbor facilities are required, because the huge ore carrier must approach thereto for loading and unloading. Accordingly, the natural conditions of the harbor are predominant factors to the solution of the problems. Therefore, the land transportation expense comprises a major portion of the total transportation expense.
b. Wet-loading and wet-unloading system
This system is designed to solve the problems of high transportation expense required for transporting iron-ore from a mine to an ore carrier. In this system, iron-ore in fine powder form is mixed with water and a pipe line is laid from a mine to a shipping harbor, and if required, the pipe line may be extended to the offing for loading the carrier with iron-ore in a slurry state. This provides very simple and economical facilities for the intended purpose, thereby reducing the expense of transportation to a great extent. However, the disadvantages thereof offset the above benefit, despite the convenience of the transportation facilities. Those disadvantages are as follows:
1. A large reservoir or pond is needed near the shipping harbor for storing a great amount of iron-ore in a slurry state for subsequent loading, as opposed to the simple land-piling of iron-ore of the former system. Thus, a broad site is required for such reservoirs.
2. At the unloading harbor, a large dehydrating facility is required for handling the bulky iron-ore in its slurry state. This requires the same scale of harbor facilities and unloading equipment as those used in the former system, and thus leads to duplicate investment.
3. During the long period of sailing of the iron-ore carrier, the iron-ore in a slurry state loaded in the carrier sediments by its gravity and then consolidates.
This unfavorable phenomenon is an extremely troublesome problem which is experienced in the transportation of the slurry ore. More particularly, once the iron-ore is loaded in the hold of a carrier, the iron-ore particulates begin with sedimentation at a relatively higher rate, while being accelerated due to the pressure or gravity of the upper layer of the slurry, with the result that the water content of the slurry is reduced from 30 to 40% at the time of loading to about 14% before sailing. As time goes on, the slurry in the hold of the carrier is further consolidated with the aid of the vibration, pitching and rolling of the carrier. As a result, the water content in the slurry is reduced further to about 7% to 8%. This value is naturally dependent on the time period of the navigation, but it has been found to range from 8% to 10% for normal sailing periods. The water content in the slurry exhibits gradual decrease from the top to the bottom of the slurry body due to the gravity of the slurry, thus leaving above the top layer of the slurry the water which has been wrung out from the slurry body due to its gravity sedimentation. The slurry body consolidated in this manner thus presents a considerably great resting angle or stability of shape, and therefore the sedimented slurry body may not crumble even if it remains in the form of a vertically extending wall along the sidewalls of the hold of the carrier, although it may be demolished by driving a tool having a sharp edge thereinto.
Meanwhile, such a consolidated slurry body may be again restored to a slurry state by spraying water thereinto under pressure to transport it to a refinery a long distance away from the unloading harbor. However, this attempt apparently results in extremely higher expense of the transportation facilities with considerable difficulties and thus is impracticable.
With those difficulties in mind, further description of the background of the invention will now be given.
When the gravity sedimented and consolidated slurry body contained in a hold is unloaded with a grab-bucket of the conventional type, there are many difficulties, because of the uniformity or levelled top surface of the slurry body and its compactness.
Therefore, in this invention, the slurry body may be unloaded by using grab-buckets of a heavy-duty type, while leaving a slurry body of a wall form along the sidewalls of the hold of the carrier. The wall of the slurry body which is left remaining is caused by the failure of the grab-buckets to be able to reach the sidewalls of the hold, which in turn results from the poor hatch design and the like, Generally, the amount of such remaining slurry body corresponds to about 30 to 40% by volume of the total slurry body.
It is dangerous for an operator, however, to demolish such a slurry body of a wall form which remains along the sidewalls of the hold of a carrier, when having recourse to conventional tools, such as a backdozer.